1. Field of the Invention
This invention relates to dental tools and more particularly to right angle dental hand pieces, also known as prophys, which are hand held in use while being power driven from a separate rotary power source, conventional per se.
2. Description of the Prior Art
Hand held dental tools which are arranged at an angle, usually at a right angle, with respect to a handle portion through which rotary power is delivered to drive the tool are most commonly gear driven with meshed gears in right angle or other angular arrangement at the head of the tool body. In use of such intermeshed gear drives, the driven tool, such as a soft rubber scrubber in common use for the cleaning of teeth, can become overheated, causing patient pain, and there is risk of the gear teeth breaking if the tool becomes jammed or restricted in its rotation with the result that too much torque is applied to the gear teeth.
Also known is a hand held dental tool drive of a more or less right angle configuration which involves a coiled spring in the drive train, such as disclosed in Freeman U.S. Pat. No. 745,722. However, in the Freeman tool the coiled spring in the drive train from the drive shaft to the tool is keyed at one end to the drive sprindle and also keyed at the other end to the tool so there is no relief in the drive train from over-torquing and overheating at the tool in the event of excessive pressure at the tool or drag on the tool.
Also known in right angle drive hand held dental tools is an arrangement Where the right angle drive is applied through a flexible cable, as in Hopkins U.S. Pat. No. 3,757,419. However, in the Hopkins drive arrangement, the flexible drive cable if fixedly attached to the motor drive shaft at its driven end and fixedly attached to the tool connector element at its driving end so that it has a like limitation as to a lack of relief from over-torquing in a manner similar to that characteristic of the Freeman drive arrangement.
Also known is a dental tool angle drive arrangement as in Nelsen et al U.S. Pat. No. 3,472,045, in which the interconnection between a drive shaft and the dental tool is by means of an elastomeric shaft with rigid interconnection to a drive shaft at one end and to a tool coupler at the other end. In the forms of elastomeric drive shafts as disclosed and discussed in said Nelsen et al U.S. patent, the drive shafts are described as being in frictional engagement with the defining surface of the housing bore in which they rotate. Such arrangements inherently generate friction and heat in the hand piece during use, in addition to being subject to unrelieved torque load in the event of excess pressure being applied to the tool.
Known as well is use in a dental hand piece of a spiral spring as a tool holder, such as in the hand piece disclosed in Bailey U.S. Pat. No. 4,021,918. However, in the Bailey arrangement, while the dental instrument such as a drill is held in the hand piece by tightening of the coils of a spring around the shank of the instrument, the drive train down to the tool holder itself involves conventional right angle related toothed gears or a conventional air driven turbine drive.